Cautionary Tale - Check you fires, check you flues

[Briss]

I suppose that British Standard BS 8511:2010 Code of practice for the installation of solid fuel heating and cooking appliances in small craft being £198 isn't going to appeal to anyone trying to fit out a narrowboat on a tight budget... or on the cheap!

 

It's pertinent to know that, although the code isn't compulsory, it will always be referred to if an accident occurs. 

 

A few bits from the code....  I don't think the OP's flue was following the code. Captain Barbossa's excuse wouldn't go down too well in court, me thinks.

• Fully insulated flue.
• Check with the makers, but insulated pipe often needs to be 3/4 of its diameter away from unprotected combustibles
• If there has to be a short length of un-insulated pipe to connect to the insulated chimney, then at least 3x its diameter away from unprotected combustibles.

[Ronaldo47]

The problem  could be partly down to the fact that thin metal is less able to  conduct heat along its length than thick metal. Thus if a part of  the surface is covered,  the covering will reduce the abiity of the covered portion to lose heat by radiation and convection,  and so its temperature will rise to a higher value than similarly-covered thicker-walled metal, which will be able to transfer heat by lateral conduction to adjacent parts that are not covered.  Thus the temperature of the covered part of the wall of a cast iron flue should be lower than the covered portion of a thin-walled flue. 

 

I have no experience of chimney flues, but I have observed that  thin stainless steel saucepans  will readily  burn stuff like custard, or even potatoes, when used on a gas stove, where the heat comes from localised very hot flames, whereas the thicker-walled aluminium and copper-bottomed stainless steel saucepans never cause burning. I presume this is because their thick metal readily conducts heat lateraly away from the location of the hottest part of the flames to less-hot areas.

 

Conversely the relatively high thermal impedance of thin metal, means that heat is less able to flow laterally from the location of the flames to the cooler areas, meaning that the flame areas impacted by the flames will get much hotter when viscous or sold contents restrict the ability for heat to be removed by convection.

[LadyG]

2 hours ago, magpie patrick said:

A useful warning - many of us rely on the idea that whoever did it "knew what they were doing" [because we probably don't]  and that a BSS catches everything - it doesn't. 

Absolutely. 

My first night on board the deckhead and smouldering paint smell woke me up at 02.00.

I dropped the register circle (I think, it's a circle of metal makes the flue to deckhead look neat?)  and attacked the fireclay, repeat Fireclay, underneath with a chisel to form an air gap (now fire rope) 

I was not able to put the very hot stove out, but closed up the air locks, and waited till it went down. 

The hearth was far too short, and the front grid of fire too low to retain coals, so I had an angle iron surround made to retain embers. This is similar to extending the hearth. 

No carpet, no rugs near the fire. 

There is no silicate board as far as I can see, it's all done on the cheap, and any assumption that the fitter knew what he was doing should be questioned. 

I will buy another extinguisher this year to have handy, It's really hard to think things through instantly, so your fire plan must be thought through now. 

Obviously the BSC does not save every life. Look after number one. 

I need another fire alarm, the ones with a bright alarm light are best imho. 

I have wound glass fibre tape round the register ring, and put more fire rope in the space. I think I should put fire rope in the collar from outside, but I'm not sure, there seems to be a small amount of fibreglass insulation, not convinced of its purpose? 

 

Edited December 1, 2021 by LadyG

[IanD]

19 minutes ago, Ronaldo47 said:

The problem  could be partly down to the fact that thin metal is less able to  conduct heat along its length than thick metal. Thus if a part of  the surface is covered,  the covering will reduce the abiity of the covered portion to lose heat by radiation and convection,  and so its temperature will rise to a higher value than similarly-covered thicker-walled metal, which will be able to transfer heat by lateral conduction to adjacent parts that are not covered.  Thus the temperature of the covered part of the wall of a cast iron flue should be lower than the covered portion of a thin-walled flue. 

 

I have no experience of chimney flues, but I have observed that  thin stainless steel saucepans  will readily  burn stuff like custard, or even potatoes, when used on a gas stove, where the heat comes from localised very hot flames, whereas the thicker-walled aluminium and copper-bottomed stainless steel saucepans never cause burning. I presume this is because their thick metal readily conducts heat lateraly away from the location of the hottest part of the flames to less-hot areas.

 

Conversely the relatively high thermal impedance of thin metal, means that heat is less able to flow laterally from the location of the flames to the cooler areas, meaning that the flame areas impacted by the flames will get much hotter when viscous or sold contents restrict the ability for heat to be removed by convection.

Except that the whole interior of the flue is heated by the hot gases, so it all gets hot. Thin stainless pans do burn stuff on a gas flame because of hot spots, but that's not the case here.

 

If there's a good heat conduction path from the top of the flue through the collar to the roof, then heat will flow up the flue and be dissipated in the roof, and a thick flue will conduct more heat to the collar and run cooler than a thin one.

 

If there isn't such a path to get rid of heat a thick flue will run almost as hot as a thin one -- but not quite because the flue above the roof helps dissipate heat too, in the same way that the collar/roof does, in fact this may be more effective.

 

However in both cases the bottom section of the flue nearest the stove will hardly be cooled at all (too far from the roof) so this is the biggest risk if you touch it.

[EdwardMeades]

1 hour ago, Tony Brooks said:

and as said that collar acts as a heat sink, conducting heat from the top end the flue to a large area on the roof where the heat can dissipate.

I thought the idea was for the flue to pass through the collar without touching it? For example a four inch flue passing through a 5 inch ID collar, then the gap is filled with rope and silicon?

[IanD]

1 minute ago, EdwardMeades said:

I thought the idea was for the flue to pass through the collar without touching it? For example a four inch flue passing through a 5 inch ID collar, then the gap is filled with rope and silicon?

I'd have thought so too, I was just going by what was said earlier. If there's no thermal contact -- which I would have thought would be A Bad Thing since it would heat the roof up and maybe scorch the paint -- it won't do much.

 

In which case the flue sticking out above the roof will help dissipate heat, but only really from the top section of the internal flue.

[Rickent]

7 minutes ago, EdwardMeades said:

I thought the idea was for the flue to pass through the collar without touching it? For example a four inch flue passing through a 5 inch ID collar, then the gap is filled with rope and silicon?

That is how I did it,  the flue doesn't touch the collar until it exits the boat, the gap is filled with fire rope, as I said the collar stays cold regardless of how hot the flue gets.

[Tony Brooks]

19 minutes ago, EdwardMeades said:

I thought the idea was for the flue to pass through the collar without touching it? For example a four inch flue passing through a 5 inch ID collar, then the gap is filled with rope and silicon?

 

It is but sometimes it will, especially if the flue and collar are at different angles. In any case glass rope will eventually conduct heat from the flue to the collar. The important is to ensure plenty of air gap between the flue/collar down-stand and any surrounding wood, plus changing and thermal insulation to a non-flammable one.

[blackrose]

6 hours ago, EdwardMeades said:

 

 

 

 

 

 

 

Glad to hear you've cut back that wood, it was far too close. Any sprayfoam in the area should be removed too. Scrape it off with a 1" chisel back to the steel. You can stuff some rockwool (glass) insulation into the area. Your new 200mm gap and double skin flu is belt & braces. My gap is about 200mm for a single skin flue.

[IanD]

6 minutes ago, Tony Brooks said:

 

It is but sometimes it will, especially if the flue and collar are at different angles. In any case glass rope will eventually conduct heat from the flue to the collar. The important is to ensure plenty of air gap between the flue/collar down-stand and any surrounding wood, plus changing and thermal insulation to a non-flammable one.

The glass rope is a very poor conductor compared to steel; the roof might warm up a bit, but it won't cool the flue down much. The hot flue sticking out into the cold air outside will have a far bigger effect.

Edited December 1, 2021 by IanD

[blackrose]

5 hours ago, MtB said:

 

I have to say, this struck me too. That flue material looks odd, like a cheap external thin steel chimney cobbled to fit. Not the 1/8" wall thickness flue tube sold by chandlers for the job. 

 

Looks like vitreous enamel to me and in my opinion it's unsuitable for a flue inside a boat. As it's difficult to buy vitreous enamel flue pipe in lengths greater than 1.2m it's generally made up of separate (unsupported?) sections. That's fine for a house, but one good whack of a boat against a lock wall and the joints between unsupported sections of flue pipe may crack without one knowing anything about it, which then leads to the possibility of CO poisoning when the stove is next lit. I hope the OP's new double skin flue is in one piece.

Edited December 1, 2021 by blackrose

[MichaelG]

My flue at the ceiling as it enters the collar passes through a square section of what looks like a hard asbestos type material , although I doubt it’s asbestos as the boat was built in 2007. 

[Midnight]

Never mind DIY fitouts when we were at Ripon the boat next to me had similar issues on both the central heating pipe and the engine exhaust both being too close to the ceiling woodwork.  The boat having been 'professionally' fitted out by a well-known boatyard in the Midlands.  The second incident happened on the tidal Ouse when the exhaust got rather hot as the engine pushed against the flood tide. It was our first trip on the tide and the owner wouldn't go inside to tackle the fire so I had to persuade my other half to steer (for the first time) while I pulled the boat alongside, crawled in through the engine room side hatch and chopped the roof panels out with an axe. The owner having sprayed the fire extinguishers all over the engine. There were a few disappointed gongoozlers at Selby expecting to see charred bodies and a burnt out boat.

[PD1964]

As the op says it’s basically his fault, so respect for being honest. If you read his previous Posts he says he has just bought a new stove with a 5” flue and is asking questions about getting a roof collar for it to pass through. He’s basically fitted a 5” flu into a roof hole that was initially for a 4” and has not trimmed the T&G away sufficiently on the left side leaving it touching flu, then just covered it with the plate, sort of blames the plate for heat transfer, but looking at his pic the wood is clearly touching the new fitted flue.

  Also looking at the photo of the Flue it looks too close to the T&G wood bulkhead to the right, with little air gap. Looks like the new fire he’s fitted has been moved right nearer the wall as this would be easier then trimming the roof hole to the left and leaving the fire central on the hearth. Looks like a bigger fire has been fitted compared to the original, hence the safety issues with insufficient air gaps.
 The lesson here is to all the Newbies buying boats and fitting new fires, is leave it to the people that do it for a living and know what their doing or if you self fit get the former to inspect for mistakes like this. A lesson learnt that could of been a lot worse and hopefully he’ll make good.

Edited December 1, 2021 by PD1964

[Peanut]

How you use your stove will make a difference too.  If you are parsimonious with your ovals the flue will be cooler than if you stoke the fire right up and have the air wide open.  I have seen the flue on a bogie stove in a Nissan hut glowing red-hot at the base, where the numpties stoked the fire to the brim.

With the evidence of poor installation, I would want to look at how the stove had been installed.  There is a report, I believe on here, of the wood behind the tiles being chard through as there was no fireproof backing or air gape behind them.  The whole installation needs checking.

 

[Alan de Enfield]

7 hours ago, Peanut said:

There is a report, I believe on here, of the wood behind the tiles being chard through as there was no fireproof backing or air gape behind them.  The whole installation needs checking.

 

 

 

On my installation, even with the 'correct' Porcelain tiles, fireboard & air gap the otherside of the wooden wall was the bathroom and it was uncomfortably 'hot to the touch'. Not 'scorching hot' but hot enough to be uncomfortable.

It wasn't even a big stove, it was the 2.5Kw / 3Kw Pipsqueak stove.

 

I guess the location didn't help the heat to escape. It was in a 30ft boat & built in the place of cupboard so surrounded on 3-sides, but the heat did get out into the boat and on one occasion we did a test to see how warm we could get the boat, once we got to 50 C then we called it a day and opened the windows and doors so we could breathe.

 

There is more to fitting a SF stove than drilling a hole in the roof and sitting it on a paving slab.

 

 

 

 

[MichaelG]

When I bought my boat it still had the original stove from new, so had been in place 13 years. I realised the surround tiles were fixed directly to the ply side lining and the back of a locker. The back of the ply in the locker got very hot but there was no evidence of charring.  The stove was quite knackered so ordered a new Boatman stove and paid the guy who makes them to fit it and a new flue. I took the opportunity to refit the surround with fire board and an air gap. When I removed the old tiles quite surprisingly there was no sign of charring to the ply. The Boatman was physically smaller than the old stove so could incorporate a larger gap between stove and surround. 

[ditchcrawler]

16 hours ago, Peanut said:

How you use your stove will make a difference too.  If you are parsimonious with your ovals the flue will be cooler than if you stoke the fire right up and have the air wide open.  I have seen the flue on a bogie stove in a Nissan hut glowing red-hot at the base, where the numpties stoked the fire to the brim.

With the evidence of poor installation, I would want to look at how the stove had been installed.  There is a report, I believe on here, of the wood behind the tiles being chard through as there was no fireproof backing or air gape behind them.  The whole installation needs checking.

 

I had a friend who came back to the boat to find smoke coming from round the tiles, The wood behind them was smouldering, Luckily a couple of buckets of water killed the fire